A server is a computer connected to a network with components similar to the typical personal computer (PC) such as a microprocessor, memory chips, and disc drives. But because the server communicates with other computers, the keyboard and video display are not necessary. Also like the typical PC, the server has a power supply and needs to dissipate heat roughly equal to the total electrical power input to the device. A typical rack or cabinet is 24- to 30-in. wide, 36- to 44-in. long and 76-in high and can incorporate up to 42 U of computing equipment. “U” is a standard unit indicating the height of the computer server. Each “U” is 1.75 in. A 5 U server is 8.75 in. tall, therefore eight 5 U servers fill a 42 U rack. Like most electronic devices, the processing power and space efficiency of the servers has increased considerably in the last several years.
As the servers have become more compact and efficient, more servers can fit into the rack or cabinet rack. A 42 U cabinet installed five years ago with three U servers has a total cooling load of 3 kW to 4 kW, about one ton of cooling in six sq ft. Today, the same cabinet can be filled with 7 U blade servers having a total power consumption over 20 kW, or more than 5.5 tons of cooling for the same six sq ft. A typical corporate data center can have several hundred cabinets. For example, a legacy computer room designed for 400 2.0-kW racks has an equipment-cooling load of 800 kW of cooling. If the legacy servers in the 400 racks are replaced with 200 racks at say 12 kW each, the equipment load increases from less than 250 tons to over 680 tons with half as many racks. If all 400 racks are upgraded to 12 kW, the cooling system capacity climbs to 1,365 tons! It is imperative to master plan for ultimate power and cooling capability as well as to set an upper limit on the maximum power consumption in a singe rack or cabinet.
Supplying power with back-up or redundancy to computer systems or servers is desirable or required in certain applications. For example, it is becoming increasingly more important to provide mechanisms that minimize unscheduled “down time” in data centers. The term “high availability” (HA) computing is often used to refer to computer systems that include these mechanisms.
HA mechanisms are provided at many levels. For example, a data center may have redundant computer systems so that if one system fails, the workload can be seamlessly shifted to another system. In addition, data may be stored in a disk array subsystem that allows any single disk drive to fail without affecting the ability of the disk array subsystem to continue operating.
One of the most important aspects of HA computing is ensuring that computer circuits receive an uninterrupted supply of DC power. Typically, a loss of DC power is caused by a loss of AC power to the AC-to-DC power supplies, or a failure of an AC-to-DC power supply. Uninterruptible AC power supplies address the problem of AC power loss by providing a constant supply of AC power to AC-to-DC power supplies. Typically, uninterruptible power supplies are implemented using rechargeable batteries, and in some cases, generators.
Redundant AC-to-DC power supplies address the problem of AC-to-DC power supply failure. In the prior art, redundant power supplies have been deployed on a “per system” basis. Typically, one redundant power supply is provided for each system, which is known in the art as “N+1” redundancy.
Computer systems also use DC-DC conversion since in many cases it is more efficient to provide AC-DC conversion to a single high DC voltage (typically 48V), then bus this voltage to second stage down-converters. In many cases, these DC-DC conversion devices are also required to be redundant.